Background and Gamma-Ray Burst simulator for the ECLAIRs 2D coded-mask imaging telescope

ECLAIRs is a French project to launch a microsatellite to observe the prompt optical and X-ray emission of Gamma-Ray Bursts (GRB). In orbiting in Low Earth Orbit, the ECLAIRs optical and X-/Gamma-ray instruments will be subject to large background count rates due to the cosmic diffuse X-/gamma-ray background and the cosmic rays. The science performances are dependent on accurately determining the background level. We present here the Mass Model of the ECLAIRs 2D coded-mask imaging telescope (EMM) with a total field of view of 53° × 53°, which will work from ∼ 10 to 50 keV for the imaging system and from ∼ 10 to 600 keV for the spectral measurements. We develop a GEANT3 based simulator to estimate the background flux of the EEM. We also present the first simulated performances expected for this instrument, such as the detected GRB rate per year, the sensitivity as a function of the GRB peak energy.